Native crayfish in the rivers Wansbeck and Aln, in Northumberland, could be under threat.

Environment Agency officers warn of the danger posed by the aggressive American Signal Crayfish.

Angling clubs, conservation groups and other organisations have all been warned that the US crayfish has been discovered in the River Derwent, near Blaydon. As a result special measures have been put in place to try to halt their spread.

Agency officers were informed by staff at Gateshead's Thornley Woods Centre that they had found two Signals - one alive and one dead.

Further surveys revealed another female signal, at Thornley Woods, which was removed by Agency staff.

Agency conservation officer Anne Lewis said: "The signal seems present in the Derwent in low numbers but it is essential we take every step to prevent their spread. The American species carries a fungal disease that has wiped out native crayfish in southern England."